During the past year a Phase I trial of recombinant leukocyte interferon in patients with a variety of disseminated cancers revealed that this agent could be administered up to doses of 50 x 10 to the six units/m squared i.m. 3 times weekly without unacceptable myelotoxicity or hepatic toxicity. This trial also showed objective evidence of antitumor response (partial remissions) in some patients with non-Hodgkin's lymphoma, breast cancer, chronic lymphocytic leukemia and Hodgkin's disease. Immunologic monitoring of patients receiving this agent failed to reveal any dose-dependent immunologic effect which correlated with tumor response. It was therefore decided to initiate Phase II efficacy trials of recombinant leukocyte interferon at a maximum tolerated dose with dose reductions as necessary for unacceptable toxicity. Phase II efficacy trials were initiated in patients with various lymphoproliferative disorders including non-Hodgkin's lymphoma, chronic lymphocytic leukemia and mycosis fungoides, as well as patients with refractory metastatic breast cancer. These trials are currently ongoing and results with regard to antitumor response and toxicity will be analyzed.